Celestron 22067 Instruction Manual

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I 10

TELESCOPE BASICS

A telescope is an instrument that collects and focuses light. The nature of the optical design determines how the light is

focused. Some telescopes, known as refractors, use lenses, .and other telescopes, known as reﬂ ectors (Newtonians), use

mirrors.

Developed in the early 1600s, the refractor is the oldest telescope design. It derives its name from the method it uses

to focus incoming light rays. The refractor uses a lens to bend or refract incoming light rays, hence the name (see Figure

3-1). Early designs used single element lenses. However, the single lens acts like a prism and breaks light down into the

colors of the rainbow, a phenomenon known as chromatic aberration. To get around this problem, a two-element lens,

known as an achromat, was introduced. Each element has a different index of refraction allowing two different wave-

lengths of light to be focused at the same point. Most two-element lenses, usually made of crown and ﬂ int glasses, are

corrected for red and green light. Blue light may still be focused at a slightly different point.

Figure31

A

cutawayviewofthelightpathofthe

cutawayviewofthelightpathofthe

Refractor

Refractor

optical

design

iMage orientation

The image orientation changes depending on how the eyepiece is inserted into the telescope. When using a star diagonal

with refractors, the image is right-side-up, but reversed from left-to-right (i.e., mirror image). If inserting the eyepiece direct-

ly into the focuser of a refractor (i.e., without the diagonal), the image is upside-down and reversed from left-to-right (i.e.,

inverted). However, when using the AstroMaster refractor and the standard erect image diagonal, the images is correctly

oriented in every aspect.

Imageorientationasseenwiththe

unaidedeye&usingerecting

devicesonrefractors&Newtonians

Invertedimage,normalwith

Newtonians&asviewedwith

eyepiecedirectlyinarefractor

Reversedfromlefttoright,as

viewedusingaStarDiagonalon

arefractor



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Celestron 22067 AstroMaster LT 80AZ Telescope